A recursive coronal hole

In the 'K-index versus time'-graph (Fig 1), visualizing the disturbances of the earth magnetic field in Wingst (Germany), you can see the recursive pattern of a coronal hole (indicated by the two green circles). A period of 27 days is approximately with the time the Sun needs to turn once around her axis.
Checking the graphs of SOHO/CELIAS and ACE , we see that the peaks in the density graph (CELIAS, Fig 3) and a more negative B_z component of the interplanetary magnetic field (ACE, Fig 4) coincide with the 2 periods of geomagnetic disturbances. The second period was less fierce in terms of the length in time as the solar input was less strong: a smaller density peak and a less negative B_z component compared with the first period. However, the k-index in Wingst reached the value of 6 compared with a 5 in the first period. The estimated K_p index from NOAA (Fig 2 ) however behaved differently. The global index reached only a 5 during the second period compared with a 6 in the first period.

Click on the Figures to enlarge.
Fig 1 Fig 2
Fig 3 Fig 4